2,2-Dimethylpentane is one of the

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. ...

s of

heptane Heptane or ''n''-heptane is the straight-chain alkane with the chemical formula H3C(CH2)5CH3 or C7H16. When used as a test fuel component in anti-knock test engines, a 100% heptane fuel is the zero point of the octane rating scale (the 100 poi ...

. It is also called neoheptane as it contains the (CH₃)₃C grouping. It has the most extreme properties of the isomers.

Preparation

A method to produce high purity 2,2-dimethylpentane is to react the grignard reagent of

n-propyl bromide 1-Bromopropane (''n''-propylbromide or nPB) is an organobromine compound with the chemical formula CH3CH2CH2Br. It is a colorless liquid that is used as a solvent. It has a characteristic hydrocarbon odor. Its industrial applications increased dr ...

(CH₃CH₂CH₂MgBr) with

tert-butyl chloride ''tert''-Butyl chloride is the organochloride with the formula . It is a colorless, flammable liquid. It is sparingly soluble in water, with a tendency to undergo hydrolysis to the corresponding ''tert''-butyl alcohol. It is produced industrial ...

((CH₃)₃CCl). ''n''-PrMgCl can be used instead of the bromide.

Properties

In 1929

Graham Edgar Graham and Graeme may refer to: People * Graham (given name), an English-language given name * Graham (surname), an English-language surname * Graeme (surname), an English-language surname * Graham (musician) (born 1979), Burmese singer * Cla ...

and

George Calingaert George may refer to: People * George (given name) * George (surname) * George (singer), American-Canadian singer George Nozuka, known by the mononym George * George Washington, First President of the United States * George W. Bush, 43rd Preside ...

made 2,2-dimethylpentane and measured its physical characteristics for the first time. The measurements were at 20 °C, not the standard conditions used in later times. For 2,2-dimethylpentane they measured a density of 0.6737 at 20 °C with a rate of change Δd/ΔT of 0.000855. The density and boiling are the lowest of the isomers of heptane. The

dielectric constant The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insulat ...

is 1.915, the lowest of the heptane isomers. The critical temperature is 247.7 °C and critical pressure 28.4 atmospheres. The refractive index at 20° is 1.38233, the same as for 2,4-dimethylpentane, equal lowest for the heptane isomers. The adiabatic compressibility is 0.0001289 and isothermal compressibility is 0.00016279 atmospheres, highest for the heptanes. The velocity of sound is 1.080 km/s which is lowest of the heptanes.

Coefficient of thermal expansion Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions. Temperature is a monotonic function of the average molecular kinetic ...

is 0.001268/°, highest of the heptanes. Surface tension is 17.80 dynes/cm.

Viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

is 0.00385. The

heat of combustion The heating value (or energy value or calorific value) of a substance, usually a fuel or food (see food energy), is the amount of heat released during the combustion of a specified amount of it. The ''calorific value'' is the total energy rele ...

is 11470 cal/g which is very similar to other heptanes.

Reactions

2,2-Dimethylpentane can form a

clathrate hydrate Clathrate hydrates, or gas hydrates, clathrates, hydrates, etc., are crystalline water-based solids physically resembling ice, in which small non-polar molecules (typically gases) or polar molecules with large hydrophobic moieties are trapped i ...

with helper gas molecules. The type of clathrate formed is called "clathrate H". 2,2-Dimethylpentane was the first compound for which the structure was determined. The clathrate has 34 molecules of water per molecule, and also has xenon and hydrogen sulfide as helper molecules. The crystals are hexagonal in form and melt at 0.6 °C. This substance is important as clathrate hydrates form problems by blocking natural gas pipelines. 2,2-Dimethylpentane does not react with bromine, iodine, nitric acid or

chlorosulfonic acid Chlorosulfuric acid (IUPAC name: sulfurochloridic acid) is the inorganic compound with the formula HSO3Cl. It is also known as chlorosulfonic acid, being the sulfonic acid of chlorine. It is a distillable, colorless liquid which is hygroscopic an ...

because there are no tertiary carbon atoms (a carbon atom with only one hydrogen attached). Heating alkanes over an aluminium trichloride is used to reform to make different isomers. 2,2-Dimethylpentane does not participate in this process and so cannot be reformed, or created by reforming other heptanes.

Natural occurrence

2,2-Dimethylpentane exists in some crude oils at low levels of about 0.01%.

References

{{DEFAULTSORT:Dimethylpentane, 2- Alkanes